1. Field of the Invention
The present invention relates to the field of wireless communication devices. More specifically, the invention relates to E911 emergency call origination behavior of the wireless communication device.
2. Related Art
In the United States, Enhanced 911 (E911) service is provided to users of wireless communication devices, also referred to herein as mobile devices, wireless devices, etc. Since May 19, 2005, the U.S. Federal Communications Commission (FCC) has mandated that when a mobile device user dials 911, the standard number for requesting help in an emergency, the wireless service provider must provide the telephone number of a 911 caller, the location of the antenna receiving the call to a local Public Safety Answering Point (PSAP), and precise information about the caller's location, usually to within 50 to 300 meters.
Current implementations of call origination present potential problems of immediate connection of an E911 call as shown in FIG. 4A. In step 400, a wireless communication device attempts to originate the E911 call on a first system. If the system is available, the call originates on the system 406. However, the system may send a global service redirection message (GSRM) to the wireless communication device 402 indicating, for example, that a particular requested origination channel is being serviced, or is otherwise temporarily unavailable for use. The GSRM received by the device includes a “redirect list”, step 408. The device then scans for available systems on the redirect list, step 410. In this prior art system configuration, when a wireless communication device fails to acquire any system of the redirect list 412, then the wireless device continues in loop scanning of the redirect list if the device continues to receive the GSRM. Thus, under some circumstances, the wireless device will fail to connect the E911 call. The loop will only end if the call originates on the first system 406 or originates on a system from the redirect list 414.
A similar situation occurs when the phone is in Emergency Call Back Mode (ECBM) as shown in FIG. 4B. A device enters ECBM, step 422, once an E911 call is connected, step 420. In this mode, the device idles on the system to stay available for a call back from the PSAP. In an example prior art scenario, a device is waiting in ECBM, and receives a GSRM, block 424. The mobile device will honor the GSRM message and attempt to connect on an alternate system according to a received redirect list, step 426. If a redirect system is available, block 428, then the device latches onto the redirect system, step 432. If all systems on the redirect list are not available, then the device continues in a search loop of the redirect list to acquire a system upon repeatedly receiving a GSRM from the first system. Because the device is ping-ponging between the directing system and the redirected systems, the PSAP cannot reach the mobile device.
The above described inherent deficiencies of the prior art system cannot ensure that a user in an emergency situation will obtain E911 assistance. Thus, a method for ensuring call connection in emergency call situations while maintaining compatibility with the existing system infrastructure is required.